The development of techniques for the isolation and in vitro culture of multipotent neural stem cells (for example, see U.S. Pat. Nos. 5,750,376; 5,980,885; 5,851,832) significantly improved the outlook for the treatment of neurodegenerative diseases and conditions. It was discovered that fetal brains can be used to isolate and culture multipotent neural stem cells in vitro. Moreover, in contrast to the long held belief that adult brain cells are not capable of replicating or regenerating brain cells, it was found that neural stem cells may also be isolated from brains of adult mammals. These stem cells, either from fetal or adult brains, are capable of self-replicating. The progeny cells can again proliferate or differentiate into any cell in the neural cell lineage, including neurons, astrocytes and oligodendrocytes. Therefore, these findings not only provide a source of neural cells which can be used in transplantations, but also demonstrate the presence of multipotent neural stem cells in adult brain and the possibility of producing neurons or glial cells from these stem cells in situ.
Certain molecules have been found to increase the number of neural stem cells in vitro or in vivo (see, e.g., U.S. Patent Application Publication Nos. 20050245436, 20040136967, 20040092448, 20030095956, 20030054998, 20030054551, 20030049838, 20030049837). The mechanisms for such increase may include stimulating proliferation, inhibiting differentiation, and/or preventing death of the neural stem cells. These molecules can thus be employed to produce neural stem cells, hence neurons and glial cells, in subjects in need of these cells.